1. Field of the Invention
The present invention relates generally to generators of referenced signals and applications thereof.
2. Description of the Related Art
The accuracy of many electronic systems is degraded if reference generators cannot efficiently supply reference signals that are stable under various operational conditions which include rapidly varying load impedances, large transient current demands, and varying supply voltages.
An exemplary reference generator application is for use in a pipelined analog-to-digital converter system. Such systems are configured with successive converter stages which each convert an analog input signal to respective digital bits of a final digital code that corresponds to the analog input signal. Except for a final converter stage, each converter stage also passes a residue signal to a succeeding stage for further conversion processing.
The residue signal is the difference between the analog signal presented to the stage and the analog equivalent of this stage's respective digital bits. Errors in generation of the residue signal cannot be corrected and, accordingly, they contribute directly to errors in the corresponding digital code.
The residue signal is often generated in switched-capacitor versions of a multiplying digital-to-analog converter (MDAC). In these MDACs, capacitors are switched in a first portion of each sample period to receive a charge from the residue signal of the preceding converter stage and switched in a second portion of each sample period to transfer this charge to an output capacitor. These charging and transferring processes are generally accomplished with the aid of reference signals from a reference generator and the accuracy of these processes is dependent upon the ability of the generator to maintain the accuracy of its reference signals in the presence of various operational conditions.